Oxidative stress is defined as an imbalance between antioxidant and reactive oxygen species (ROS) in favour of the latter. ROS, which include free radicals, are continuously produced in the body and play an important physiological role at low concentrations. They act as second messengers capable of modulating the expression of various genes involved in immune response. Various conditions, e.g. sun exposure, intense exercise, smoking habits, chronic inflammation, metal poisoning, mitochondrial dysfunction, or hyperglycaemia can, however, lead to a non-physiological production of ROS and will cause irreversible cell lesions that are linked to the development of several human pathologies including, atherosclerosis, cardiovascular disease, cancer, diabetes complications, muscular degeneration and arthritis.
Since the discovery that oral progestational 19-nor steroids could inhibit ovulation (Chang et al, Science 1956 124; 890-891), several million woman have used different types of synthetic estrogens and progestins to prevent conception. In post-menopausal women, hormone replacement therapy (HRT) is based on the intake of different types of hormones involving estrogens (namely estradiol and conjugated estrogens) and natural progesterone or synthetic progestins in order to replace the failing ovarian secretion.
Apart from their gynaecologic influence, the hormones have been shown to affect a number of metabolic and nutritional processes, some advantageously and others disadvantageously. Their relationship with oxidative stress has been a matter of ongoing discussion. Estrogens are recognized to be beneficial in the prevention of atherosclerosis although they are capable of inducing oxidative stress, which is involved in the development of the same atherosclerosis. A recent study (Pincemail et al., Human Reproduction 2007; 2335-2343), indicates that the intake of estrogens is associated with a significantly altered Oxidative Stress among women aged 40-48 years.
The objective of the present invention is to provide a therapy to reduce the oxidative stress induced pathologies, hereinafter also referred to as ROS induced pathologies, which for example results in a increased lipid peroxidation, in subjects in need thereof; in particular to reduce ROS induced pathologies in women using oral contraceptives and in hormone replacement therapy. An improvement of oxidative stress status in said subjects can be assessed using the parameters mentioned in the clinical study hereinafter and typically include a significant reduction of the lipidic peroxides, oxidized LDL or both parameters in said subjects, preferably with a normalization of the Cu/Zn ratio.
Clinical studies as to the antioxidant effect of zinc in a variety of disease states and patient populations demonstrate that there is no uniform response throughout the different disease states and patient populations with sometimes even contradictory effects. A study to the effect of zinc supplementation on the occurrence of infections of healthy elderly people (Am. J. Clin. Nutr. 2007, 85 (3):837-44) found that the incidence of infection was significantly lower in the zinc supplemented group with a reduction in oxidative stress markers including a significant diminution of lipid peroxides. This in contrast to a more recent study as to the beneficial effects of zinc supplementation on oxidative stress markers and antioxidant defences in middle-aged and elderly people (J. Am. Coll. Nutr. 2008, 27 (4):463-9). Contrary to the previous study, zinc supplementation did not alter oxidative stress markers and had no effect on the oxidative stress status of said individuals. Similar results were found in a study to the effects of zinc supplementation on in vitro copper-induced oxidation of LDL in healthy French subjects aged 55-70 years (Br. J. Nutr., 2006, 95 (6):1134-42). Again no effects of zinc supplementation on Cu-induced LDL oxidation were found.
Even in study populations known to experience oxidative stress, such as for example in patients with chronic obstructive pulmonary disease, hypobaric hypoxia, type 2 diabetes mellitus (T2DM) and sickle cell disease patients; there is no uniform effect of zinc supplementation on oxidative stress markers and in particular on lipid peroxidation products. In the hypobaric hypoxia studies (Aviat. Space Environ. Med. 2004, 75 (10):881-8; Wilderness Eniron. Med. 1999, 10 (2):66-74) and the COPD study (Respir. Med. 2008, 102 (6):840-4) no effects were found for zinc supplementation on the oxidative stress markers in said subjects. This in contrast to the studies in T2DM (J. Am. Coll. Nutr. 2003, 22 (4):316-21) and sickle cell disease (Transl. Res. 2008, 152 (2):67-80) which suggest that zinc supplementation may be beneficial in said patients.
Despite the generally accepted fact that hydroxyl radical scavengers like flavonoids, and in particular quercetin, are potent antioxidants in vitro, with quercetin being the most effective inhibitor of oxidative damage to LDL in vitro, numerous studies indicate that this effect is absent in vivo. See for example the study on the effects of a high flavonoid diet in healthy volunteers (Free Radic. Res. 2000, 33 (4):419-426) where no significant difference was found in the Cu2+ ion-stimulated lag-time of LDL oxidation between the high and low flavonoid dietary treatments. In another study in normocholesterolaemic female volunteers (Eur. J. Clin. Nutr. 2000, 54 (10):774-82), a 6 week rutin supplementation significantly elevated the levels of three plasma flavonoids but had no effect on plasma antioxidant status. Even in study populations with oxidative damage/stress, such as for example in athletes with exercise-induced damage and inflammation (Appl. Physiol. Nutr. Metab. 2008, 33 (2):254-62) or in hypertensive subjects, including both men and women (J. Nutr. 2007, 137 (11):2405-2411), quercetin supplementation does not exert protection from oxidative stress induced damage, and does not result in a reduction of systemic markers of oxidative stress in said studies. This different behaviour of hydroxyl radical scavengers like flavonoids, and in particular quercetin, in an in vivo environment vis-à-vis an ex vivo (in vitro) environment was also found in a study to investigate whether in vivo supplementation with red wine extracts and quercetin can have an effect on the oxidative resistance of LDL (Clin. Chem. 2000, 46 (8 Pt1):1162-70). In this study no effects were found for the parameters directly assessed in the plasma of said patients, but only for an ex vivo determination of the LDL oxidizability.